Improving hemocompatibility in tissue-engineered products employing heparin-loaded nanoplatforms

The enhancement of hemocompatibility through the use of nanoplatforms loaded with heparin represents a highly desirable characteristic in the context of emerging tissue engineering applications. The significance of employing heparin in biological processes is unquestionable, owing to its ability to interact with a diverse range of proteins. It plays a crucial role in numerous biological processes by engaging in interactions with diverse proteins and hydrogels. This review provides a summary of recent endeavors focused on augmenting the hemocompatibility of tissue engineering methods through the utilization of nanoplatforms loaded with heparin. This study also provides a comprehensive review of the various applications of heparin-loaded nanofibers and nanoparticles, as well as the techniques employed for encapsulating heparin within these nanoplatforms. The biological and physical effects resulting from the encapsulation of heparin in nanoplatforms are examined. The potential applications of heparin-based materials in tissue engineering are also discussed, along with future perspectives in this field.

Exploring nanocellulose frontiers: A comprehensive review of its extraction, properties, and pioneering applications in the automotive and biomedical industries

Material is an inseparable entity for humans to serve different purposes. However, synthetic polymers represent a major category of anthropogenic pollutants with detrimental impacts on natural ecosystems. This escalating environmental issue is characterized by the accumulation of non-biodegradable plastic materials, which pose serious threats to the health of our planet's ecosystem. Cellulose is becoming a focal point for many researchers due to its high availability. It has been used to serve various purposes. Recent scientific advancements have unveiled innovative prospects for the utilization of nanocellulose within the area of advanced science. This comprehensive review investigates deeply into the field of nanocellulose, explaining the methodologies employed in separating nanocellulose from cellulose. It also explains upon two intricately examined applications that emphasize the pivotal role of nanocellulose in nanocomposites. The initial instance pertains to the automotive sector, encompassing cutting-edge applications in electric vehicle (EV) batteries, while the second exemplifies the use of nanocellulose in the field of biomedical applications like otorhinolaryngology, ophthalmology, and wound dressing. This review aims to provide comprehensive information starting from the definitions, identifying the sources of the nanocellulose and its extraction, and ending with the recent applications in the emerging field such as energy storage and biomedical applications.

Current Strategies for Engineered Vascular Grafts and Vascularized Tissue Engineering

Blood vessels not only transport oxygen and nutrients to each organ, but also play an important role in the regulation of tissue regeneration. Impaired or occluded vessels can result in ischemia, tissue necrosis, or even life-threatening events. Bioengineered vascular grafts have become a promising alternative treatment for damaged or occlusive vessels. Large-scale tubular grafts, which can match arteries, arterioles, and venules, as well as meso- and microscale vasculature to alleviate ischemia or prevascularized engineered tissues, have been developed. In this review, materials and techniques for engineering tubular scaffolds and vasculature at all levels are discussed. Examples of vascularized tissue engineering in bone, peripheral nerves, and the heart are also provided. Finally, the current challenges are discussed and the perspectives on future developments in biofunctional engineered vessels are delineated.

Sustainable Applications of Nanofibers in Agriculture and Water Treatment: A Review

Natural fibers are an important source for producing polymers, which are highly applicable in their nanoform and could be used in very broad fields such as filtration for water/wastewater treatment, biomedicine, food packaging, harvesting, and storage of energy due to their high specific surface area. These natural nanofibers could be mainly produced through plants, animals, and minerals, as well as produced from agricultural wastes. For strengthening these natural fibers, they may reinforce with some substances such as nanomaterials. Natural or biofiber-reinforced bio-composites and nano–bio-composites are considered better than conventional composites. The sustainable application of nanofibers in agricultural sectors is a promising approach and may involve plant protection and its growth through encapsulating many bio-active molecules or agrochemicals (i.e., pesticides, phytohormones, and fertilizers) for smart delivery at the targeted sites. The food industry and processing also are very important applicable fields of nanofibers, particularly food packaging, which may include using nanofibers for active–intelligent food packaging, and food freshness indicators. The removal of pollutants from soil, water, and air is an urgent field for nanofibers due to their high efficiency. Many new approaches or applicable agro-fields for nanofibers are expected in the future, such as using nanofibers as the indicators for CO and NH3. The role of nanofibers in the global fighting against COVID-19 may represent a crucial solution, particularly in producing face masks.

The performance of heparin modified poly(ε-caprolactone) small diameter tissue engineering vascular graft in canine-A long-term pilot experiment in vivo

Long-term in vivo observation in large animal model is critical for evaluating the potential of small diameter tissue engineering vascular graft (SDTEVG) in clinical application, but is rarely reported. In this study, a SDTEVG is fabricated by the electrospinning of poly(ε-caprolactone) and subsequent heparin modification. SDTEVG is implanted into canine's abdominal aorta for 511 days in order to investigate its clinical feasibility. An active and robust remodeling process was characterized by a confluent endothelium, macrophage infiltrate, extracellular matrix deposition and remodeling on the explanted graft. The immunohistochemical and immunofluorescence analysis further exhibit the regeneration of endothelium and smooth muscle layer on tunica intima and tunica media, respectively. Thus, long-term follow-up reveals viable neovessel formation beyond graft degradation. Furthermore, the von Kossa staining exhibits no occurrence of calcification. However, although no TEVG failure or rupture happens during the follow-up, the aneurysm is found by both Doppler ultrasonic and gross observation. Consequently, as-prepared TEVG shows promising potential in vascular tissue engineering if it can be appropriately strengthened to prevent the occurrence of aneurysm.

Fabrication and characterization of conductive polypyrrole/chitosan/collagen electrospun nanofiber scaffold for tissue engineering application

Conductive electrospun nanofiber scaffold containing conductive polypyrrole (PPy) polymer was fabricated to accelerate healing of damaged tissues. In order to prepare these scaffolds, various weight percentages of polypyrrole (5, 10, 15, 20, 25%) relative to the polymers combination (chitosan, collagen, and polyethylene oxide) were used. The fabricated composite scaffolds were characterized using chemical, morphological, physio-mechanical, and biological analyses including; FTIR spectroscopy, SEM, electrical conductivity, tensile test, in vitro degradation, MTT Assay and cell culture. The polypyrrole particles were perfectly dispersed inside the nanofibers, and the fibers average diameter were reducing by increasing the polypyrrole content in the composites. The presence of polypyrrole in fibers enhanced their conductivity up to 164.274 × 10^-3 s/m which is in the range of semi-conductive and conductive polymers. MTT and SEM analyses displayed that nanofibers composing 10% polypyrrole possess better cell adhesion, growth and proliferation properties comparing to other compositions. Furthermore, the suitable mechanical properties of scaffolds ideally fitted them for different kinds of tissue applications including skin, nerve, heart muscle, etc. Therefore, these fabricated conductive nanofiber scaffolds are particularly appropriate for employing in body parts with electrical signals such as cardiovascular, heart muscles, or nerves.

Nanocellulose in biomedical and biosensing applications: A review

Cellulose is abundant in the nature and nanocellulose (NC) in particular is regarded as a credible green substrate to be used in bio nanocomposites for various applications. NC exhibits excellent mechanical reinforcement properties comparable to conventionally used materials due to its high specific surface area and tunable surface chemistry. Additionally, low toxicity, biodegradability and biocompatibility of NC deem it a promising material for use in different biomedical applications. In this review, we highlight the biomedical applications of NC based hydrogels and aerogels/nanocomposites and advancements of their employment in the areas of wound dressing, drug delivery, tissue engineering, scaffolds and biomedical implants. This review also explores the recent use of NC in making biosensors for the detection of cholesterol, various enzymes and diseases, heavy metal ions in human sweat and urine, and for general health monitoring.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

A new method for the preparation of three-layer vascular stents: a preliminary study on the preparation of biomimetic three-layer vascular stents using a three-stage electrospun membrane

There is an urgent need to design a tissue-engineered vascular graft that exhibits good biocompatibility and sufficient mechanical strength to repair and facilitate regeneration of defective vascular tissue. It is generally accepted that multi-layer stents can be used to simulate the structure and function of natural blood vessels. Here, we developed a new three-layer tubular graft that is rolled from a single Poly(L-lactide-co-caprolactone) electrospun membrane. We used a new electrospinning technique to place three different structures on a single electrospun membrane such that the stent is comprised of three different layers. The inner layer is dense and suitable for endothelial cell growth, the middle layer is a parallel loose structure suitable for smooth muscle cell growth, and the outer layer is a parallel structure with sparse alternating texture suitable for both smooth muscle cell growth and structural support. The vascular stent has good tensile strength. At the same time, endothelial cells and smooth muscle cells readily proliferate on the material in vitro. In particular, smooth muscle cells grow in parallel on the middle and outer materials. In vivo, all layers of the vascular graft were infiltrated by cells within one week of subcutaneous implantation, indicative of favorable biocompatibility. After a week of subcutaneous implantation, the vascular stent was orthotopically transplanted into the abdominal aorta of Sprague Dawley rats. After ten weeks of transplantation, ultrasound imaging of the abdomen showed vascular patency. The vascular stent was endothelialized, smooth muscle cells readily proliferated, and a large amount of elastic fibers were formed. Therefore, our specially designed tri-layer vascular graft may be of significant benefit in vascular reconstruction.

Performance of PEGylated chitosan and poly (L-lactic acid-co-ε-caprolactone) bilayer vascular grafts in a canine femoral artery model

The fabrication of a functional small-diameter vascular graft with good biocompatibility, in particular hemocompatibility, has become an urgent clinical necessity. We fabricated a native bilayer, small-diameter vascular graft using PEGylated chitosan (PEG-CS) and poly (L-lactic acid-co-ε-caprolactone; PLCL). To stabilize the inner layer, a PEG-CS blend with PLCL at ratio of 1:6 was casted on a round metal bar by a drip feed, and the outer layer, a PLCL blend with water-soluble PEG that acted as a sacrificial part to enhance pore size, was fabricated by electrospinning. The results showed excellent hemocompatibility and strong mechanical properties. In vitro, the degradation of the graft was evaluated by measuring the graft structure, mass loss rate, and changes in molecular weight. The results indicated that the graft had adequate support for the regeneration of blood vessels before collapse. An in vivo study was performed in a canine femoral artery model for up to 24 weeks, which demonstrated that the PEGylated bilayer grafts possessed excellent structural integrity, high compatibility with blood, good endothelial cell (EC) and smooth muscle cell (SMC) growth, and high expression levels of angiogenesis-related proteins, features that are highly similar to autologous blood vessels. Moreover, the results showed almost negligible calcification within 24 weeks. These findings confirm that the bilayer graft mimics native cells, thereby effectively improving vascular remodeling.

Fabrication Techniques for Vascular and Vascularized Tissue Engineering

Impaired or damaged blood vessels can occur at all levels in the hierarchy of vascular systems from large vasculatures such as arteries and veins to meso- and microvasculatures such as arterioles, venules, and capillary networks. Vascular tissue engineering has become a promising approach for fabricating small-diameter vascular grafts for occlusive arteries. Vascularized tissue engineering aims to fabricate meso- and microvasculatures for the prevascularization of engineered tissues and organs. The ideal small-diameter vascular graft is biocompatible, bridgeable, and mechanically robust to maintain patency while promoting tissue remodeling. The desirable fabricated meso- and microvasculatures should rapidly integrate with the host blood vessels and allow nutrient and waste exchange throughout the construct after implantation. A number of techniques used, including engineering-based and cell-based approaches, to fabricate these synthetic vasculatures are herein explored, as well as the techniques developed to fabricate hierarchical structures that comprise multiple levels of vasculature.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Photocrosslinkable Nanofibrous Asymmetric Membrane Designed for Wound Dressing

Recently, the biomedical scientists who are working in the skin regeneration area have proposed asymmetric membranes as ideal wound dressings, since they are able to reproduce both layers of skin and improve the healing process as well as make it less painful. Herein, an electrospinning technique was used to produce new asymmetric membranes. The protective layer was composed of a blending solution between polycaprolactone and polylactic acid, whereas the underlying layer was comprised of methacrylated gelatin and chitosan. The chemical/physical properties, the in vitro hemo- and biocompatibility of the nanofibrous membranes were evaluated. The results obtained reveal that the produced membranes exhibited a wettability able to provide a moist environment at wound site. Moreover, the membranes' hemocompatibility and fibroblast cell adhesion, spreading and proliferation at the surface of the membranes were also noticed in the in vitro assays. Such results highlight the suitability of these asymmetric membranes for wound dressing applications.

Targeted Delivery of Bioactive Molecules for Vascular Intervention and Tissue Engineering

Cardiovascular diseases are the leading cause of death in the United States. Treatment often requires surgical interventions to re-open occluded vessels, bypass severe occlusions, or stabilize aneurysms. Despite the short-term success of such interventions, many ultimately fail due to thrombosis or restenosis (following stent placement), or incomplete healing (such as after aneurysm coil placement). Bioactive molecules capable of modulating host tissue responses and preventing these complications have been identified, but systemic delivery is often harmful or ineffective. This review discusses the use of localized bioactive molecule delivery methods to enhance the long-term success of vascular interventions, such as drug-eluting stents and aneurysm coils, as well as nanoparticles for targeted molecule delivery. Vascular grafts in particular have poor patency in small diameter, high flow applications, such as coronary artery bypass grafting (CABG). Grafts fabricated from a variety of approaches may benefit from bioactive molecule incorporation to improve patency. Tissue engineering is an especially promising approach for vascular graft fabrication that may be conducive to incorporation of drugs or growth factors. Overall, localized and targeted delivery of bioactive molecules has shown promise for improving the outcomes of vascular interventions, with technologies such as drug-eluting stents showing excellent clinical success. However, many targeted vascular drug delivery systems have yet to reach the clinic. There is still a need to better optimize bioactive molecule release kinetics and identify synergistic biomolecule combinations before the clinical impact of these technologies can be realized.

Electrospun vascular grafts fabricated from poly(L-lactide-co-ε-caprolactone) used as a bypass for the rabbit carotid artery

The study involved the electrospinning of the copolymer poly(L-lactide-co-ε-caprolactone) (PLCL) into tubular grafts. The subsequent material characterization, including micro-computed tomography analysis, revealed a level of porosity of around 70%, with pore sizes of 9.34 ± 0.19 μm and fiber diameters of 5.58 ± 0.10 μm. Unlike fibrous polycaprolactone, the electrospun PLCL copolymer promoted fibroblast and endothelial cell adhesion and proliferation in vitro. Moreover, the regeneration of the vessel wall was detected following implantation and, after six months, the endothelialization of the lumen and the infiltration of arranged smooth muscle cells producing collagen was observed. However, the degradation rate was found to be accelerated in the rabbit animal model. The study was conducted under conditions that reflected the clinical requirements-the prostheses were sutured in the end-to-side fashion and the long-term end point of prosthesis healing was assessed. The regeneration of the vessel wall in terms of endothelialization, smooth cell infiltration and the presence of collagen fibers was observed after six months in vivo. A part of the grafts failed due to the rapid degradation rate of the PLCL copolymer.

The effect of ethylene oxide sterilization on electrospun vascular grafts made from biodegradable polyesters

The study describes the detailed examination of the effect of ethylene oxide sterilization on electrospun scaffolds constructed from biodegradable polyesters. Different fibrous layers fabricated from polycaprolactone (PCL) and a copolymer consisting of polylactide and polycaprolactone (PLCL) were investigated for the determination of their mechanical properties, degradation rates and interaction with fibroblasts. It was discovered that the sterilization procedure influenced the mechanical properties of the electrospun PLCL copolymer scaffold to the greatest extent. No effect of ethylene oxide sterilization on degradation behavior was observed. However, a delayed fibroblast proliferation rate was noticed with concern to the ethylene oxide sterilized samples compared to the ethanol sterilization of the materials.

Promotion of Vascular Morphogenesis of Endothelial Cells Co-Cultured with Human Adipose-Derived Mesenchymal Stem Cells Using Polycaprolactone/Gelatin Nanofibrous Scaffolds

New blood vessel formation is essential for tissue regeneration to deliver oxygen and nutrients and to maintain tissue metabolism. In the field of tissue engineering, in vitro fabrication of new artificial vessels has been a longstanding challenge. Here we developed a technique to reconstruct a microvascular system using a polycaprolactone (PCL)/gelatin nanofibrous structure and a co-culture system. Using a simple electrospinning process, we fabricated three-dimensional mesh scaffolds to support the sprouting of human umbilical vein endothelial cells (HUVECs) along the electrospun nanofiber. The co-culture with adipose-derived mesenchymal stem cells (ADSCs) supported greater sprouting of endothelial cells (ECs). In a two-dimensional culture system, angiogenic cell assembly produced more effective direct intercellular interactions and paracrine signaling from ADSCs to assist in the vascular formation of ECs, compared to the influence of growth factor. Although vascular endothelial growth factor and sphingosine-1-phosphate were present during the culture period, the presence of ADSCs was the most important factor for the construction of a cell-assembled structure in the two-dimensional culture system. On the contrary, HUVECs co-cultured on PCL/gelatin nanofiber scaffolds produced mature and functional microvessel and luminal structures with a greater expression of vascular markers, including platelet endothelial cell adhesion molecule-1 and podocalyxin. Furthermore, both angiogenic factors and cellular interactions with ADSCs through direct contact and paracrine molecules contributed to the formation of enhanced engineered blood vessel structures. It is expected that the co-culture system of HUVECs and ADSCs on bioengineered PCL/gelatin nanofibrous scaffolds will promote robust and functional microvessel structures and will be valuable for the regeneration of tissue with restored blood vessels.

Fabrication and preliminary study of a biomimetic tri-layer tubular graft based on fibers and fiber yarns for vascular tissue engineering

Designing a biomimetic and functional tissue-engineered vascular graft has been urgently needed for repairing and regenerating defected vascular tissues. Utilizing a multi-layered vascular scaffold is commonly considered an effective way, because multi-layered scaffolds can easily simulate the structure and function of natural blood vessels. Herein, we developed a novel tri-layer tubular graft consisted of Poly(L-lactide-co-caprolactone)/collagen (PLCL/COL) fibers and Poly(lactide-co-glycolide)/silk fibroin (PLGA/SF) yarns via a three-step electrospinning method. The tri-layer vascular graft consisted of PLCL/COL aligned fibers in inner layer, PLGA/SF yarns in middle layer, and PLCL/COL random fibers in outer layer. Each layer possessed tensile mechanical strength and elongation, and the entire tubular structure provided tensile and compressive supports. Furthermore, the human umbilical vein endothelial cells (HUVECs) and smooth muscle cells (SMCs) proliferated well on the materials. Fluorescence staining images demonstrated that the axially aligned PLCL/COL fibers prearranged endothelium morphology in lumen and the circumferential oriented PLGA/SF yarns regulated SMCs organization along the single yarns. The outside PLCL/COL random fibers performed as the fixed layer to hold the entire tubular structure. The in vivo results showed that the tri-layer vascular graft supported cell infiltration, scaffold biodegradation and abundant collagen production after subcutaneous implantation for 10weeks, revealing the optimal biocompatibility and tissue regenerative capability of the tri-layer graft. Therefore, the specially designed tri-layer vascular graft will be beneficial to vascular reconstruction.

Comprehensive assessment of electrospun scaffolds hemocompatibility

Biodegradable polyesters, namely polycaprolactone (PCL) and copolymer of polylactide and polycaprolactone (PLCL) were electrospun into various fibrous structures and their hemocompatibility was evaluated in vitro. Firstly, hemolytic effect was evaluated upon incubation with diluted whole blood. The results showed that the degree of hemolysis depended on chemical composition and fibrous morphology. Electrospun polycaprolactone induced slight degree of hemolysis depending on its molecular weight and fibrous morphology; copolymer PLCL did not cause detectable hemolysis. The influence of coagulation pathways was examined by measurement of coagulation times. It was showed that intrinsic coagulation pathway assessed by activated partial thromboplastin time (APTT) was moderately accelerated after incubation with PCL and prolonged after incubation with copolymer PLCL. Extrinsic activation of coagulation tested by prothrombin time (PT) was slightly accelerated after incubation with all tested electrospun samples. Thrombogenicity assessment of fibrous samples revealed high thrombogenic properties of fibrous materials that was comparable to high degree of collagen thrombogenicity. The level of platelet activation was dependent on chemical composition and surface morphology of tested materials.

Application of a bilayer tubular scaffold based on electrospun poly(l-lactide-co-caprolactone)/collagen fibers and yarns for tracheal tissue engineering

An electrospun bilayer tubular scaffold based on collagen/P(LLA–CL) was prepared and preprocessing with autologous tracheal cells and vascularization was done for the purpose of tracheal tissue engineering.

Laminin-coated nerve guidance conduits based on poly(l-lactide-co-glycolide) fibers and yarns for promoting Schwann cells’ proliferation and migration

A laminin-coated and yarn-encapsulated PLGA nerve guidance conduit for Schwann cells’ proliferation and migration.

Polypyrrole-coated poly(l-lactic acid-co-ε-caprolactone)/silk fibroin nanofibrous membranes promoting neural cell proliferation and differentiation with electrical stimulation

Polypyrrole (Ppy), as a conductive polymer, is commonly used for nerve tissue engineering because of its good conductivity and non-cytotoxicity. To avoid the inconvenience of Ppy processing, it was coated on electrospun poly(l-lactic acid-co-ε-caprolactone)/silk fibroin (PLCL/SF) nanofibers via the in situ oxidative polymerization of pyrrole monomers in this study. Ppy-coated PLCL/SF membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric (TG) analysis. The results confirmed the disposition of Ppy on the PLCL/SF nanofibers, and the nanofibers kept their nanofibrous morphology and thermal stability, in comparison to the untreated ones. The conductivities and water contact angles were evaluated as well, and indicated that the conductivity and hydrophilicity of Ppy-coated nanofibers were increased. Furthermore, this study showed that electrical stimulation (ES) promoted PC12 cell differentiation and axonal extension on Ppy-coated nanofibers. The MTT assay suggested that both Ppy and ES could promote Schwann cell (SC) proliferation. Immunofluorescence staining and real time-qPCR (RT-qPCR) testing demonstrated that ES could induce PC12 cell differentiation even without nerve growth factor (NGF) treatment, and moreover, Ppy coating increased the inducing effects on PC12 cell differentiation. The overall results indicated the promising potential of Ppy-coated PLCL/SF nanofibrous membranes for peripheral nerve repair and regeneration.